1. Field of the Invention
The present invention relates generally to power supplies and more particularly to a selectable source input power supply.
2. Description of the Related Art
In the past, power supplies each included a single power supply circuit designed for a specific operating environment (e.g., available input source type, voltage, and current ranges and required output type, voltage, and current ranges) or application. More recently, power supplies including multiple power supply circuits within a single package or design, each designed for a particular operating environment or application, have been provided. FIG. 1 illustrates a power supply including multiple power supply circuits according to the prior art.
In the illustrated embodiment of FIG. 1, a power supply 100 is depicted including an alternating current (AC) source input power supply circuit 102 and a direct current (DC) source input power supply circuit 104. AC source input power supply 102 includes an AC input connector 106 and a line filter 108 within an input stage (e.g., filtered connector 110), a voltage rectifier 112, a power factor correction (PFC) sub-circuit 114, and an isolation stage including a high voltage transistor 116, a transformer 118, a rectifier 120, and a control element 122. DC source input power supply 104 of the illustrated prior art embodiment includes an DC input connector 126 and a line filter 128 within an input stage (e.g., filtered connector 124), and an isolation stage including a low voltage transistor 130, a transformer 132, a rectifier 134, and a control element 136.
In operation, AC source input power supply circuit 102 is coupled to an AC voltage source via AC input connector 106 to receive an AC voltage. The received AC voltage is then filtered using line filter 108 to attenuate electromagnetic noise included within the supplied AC voltage. The filtered AC voltage is next full-wave rectified using rectifier 112 and applied to PFC sub-circuit 114 reducing harmonic distortion and generating a ˜400 VDC voltage. The DC voltage output from PFC sub-circuit 114 is then converted or transformed using high voltage transistor 116, transformer 118, control element 122 and rectifier 120 to a desired DC voltage. Similarly DC source input power supply circuit 104 in operation is coupled to a DC voltage source via DC input connector 126 to receive a DC voltage. The received DC voltage is then filtered using line filter 128 and converted or transformed using low voltage transistor 130, transformer 132, control element 136 and rectifier 134 to a desired DC voltage.
Power supplies, such as power supply 100 of FIG. 1, including multiple power supply circuits are capable of being coupled to a greater number of potential sources and consequently providing greater flexibility. Nevertheless, such power supplies suffer from a number of significant drawbacks. Duplicative components (e.g., input connectors 106 and 126, line filters 108 and 128, transformers 118 and 132, rectifiers 120 and 134, and control elements 122 and 136) significantly increases the overall cost of power supply 100 as compared to alternative single power supply circuit designs. Moreover, switching between alternative sources requires physical disconnection and downtime and damage may result to power supply circuits 102, 104 and/or load devices or circuits if a source is incorrectly coupled to power supply 100.
In an alternative power supply design, multiple input stages are coupled to shared portions of a power supply circuit. FIG. 2 illustrates a power supply including a shared portion of a power supply circuit and multiple input stages according to the prior art. In the illustrated embodiment of FIG. 2, a power supply 200 is depicted including an AC input connector 202 and a line filter 204 within a first input stage 206, and a DC input connector 208 and a line filter 210. Power supply 200 of the illustrated prior art embodiment further includes a voltage rectifier 214, a power factor correction (PFC) sub-circuit 216, and an isolation stage including a transistor 218, a transformer 220, a rectifier 222, and a control element 224.
In operation, AC voltages may be received from an AC voltage source coupled to power supply 200 via AC input connector 202 or DC voltages may be received from a DC voltage source coupled to power supply 200 via DC input connector 208. An AC voltage received by power supply 200 is filtered using line filter 204 to attenuate electromagnetic noise included within the supplied AC voltage. The filtered AC voltage is then full-wave rectified using rectifier 214 and applied to PFC sub-circuit 216, generating a DC voltage. The DC voltage output from PFC sub-circuit 216 is then converted or transformed using transistor 218, transformer 220, control element 224 and rectifier 222 to a desired DC voltage. Similarly, in operation a DC voltage received by power supply 200 is filtered using line filter 210 and converted or transformed using transistor 218, transformer 220, control element 224 and rectifier 222.
Although reducing somewhat the number of duplicate components as compared with power supplies including completely independent power supply circuits, power supplies such as power supply 200 of FIG. 2 still include a number of duplicate components (e.g., input connectors 202 and 208 and line filters 204 and 210) and must include specialized components due to their design which significantly increase overall cost. For example, transistor 218 of the prior art embodiment of FIG. 2 must be capable of operating when supplied both with high voltages frequently associated with higher voltage AC inputs and with high currents frequently associated with lower voltage DC inputs in order to operate correctly over a sufficiently wide input voltage range. Moreover, switching between alternative sources using the power supply design of FIG. 2 requires physical disconnection and downtime and damage may result to the power supply and/or load devices or circuits if a source is incorrectly coupled to power supply 200.